To save a message to a floppy disk or hard drive, you must use the browser's save function. The message will be saved as HTML and can be viewed later in a browser.
There is no direct way to save a plain text version of a message from WebMail.
If you want to save a plain text version of a message, you can cut and paste the text of the message into a word processor. Another option is to use an HTML editor's "strip tags" function to remove the HTML tags of a message saved by the browser.